Synchronizer circuit



Dec. 19, 1950 J. R. wlLKERsoN sYNcHRoNIzER CIRCUIT 4 Sheets-Sheet 2 Filed Oct. 22. 1943 INVENTOR R. W/KERso/V BY @MW ATTORNEY hrm.

Dec. 19, 1950 J. R. wlLKERsoN sYNcHRoNIzER CIRCUIT 4 Sheets-Sheet 3 Filed Oct. 22, 1945 ATTORNEY Dec. 19, 1950 1 R, wlLKERsoN 2,534,329

SYNCHRONIZER CIRCUIT Filed oct. 22, 194s 4 sheets-sheet 4 INVENTOR d, f? VV/L KERso/v ORNEY Patented Dec. 19, 1950 UNITED STATES PATENT OFFICE SYNCHRONIZER CIRCUIT Delaware Y Application October 22, 1943, Serial No. 507,251

Claims. l

My invention relates to electronic circuits generally and is concerned primarily with synchro- I izing circuits.

In various applications of transmission and reception, such as those made in connection with radio detecting and ranging or radar apparatus, it is necessary that the transmission of the detecting or transmitted signal be compared in time with the received or reflected signal, that the receiver be turned on and the transmitter turned off in timed relationship with each other, that the receiver be conditioned to receive selected signals only, that means be provided for accurate measurement of infinitesimal periods of time, and that many other functions be accomplished which must be timed to the micro-second. The circuit which accomplishes these` objects is referred to as a synchronizer, and it is with such that the -instant invention deals.

Accordingly, it is an object of my invention to provide a synchronizer in which the phase of a transmitted pulse is varied with respect to that of a receiver control pulse or gate.

It is also a purpose of my invention to provide an electronic circuit in which a plurality of frequency dividers are used to decrease the repetition rate of a transmitted pulse which is initiated to occur at intervals corresponding to selected points on a fixed frequency, sinusoidally varying voltage wave.

It is also an object of my invention to provide a synchronizer circuit adaptable to radar apparatus by means of which the systems range sensing apparatus may be automatically operated for range tracking.

As a further object of my invention, I wish to provide a circuit adaptable to radar apparatus which will generate a xed frequency voltage and a sweep control or gating pulse for the systems indicator circuit, a trigger pulse and a sweep control or gating pulse for its transmitter, and a narrow control or gating pulse for its receiver.

I also Wish to provide, as another object of my invention, a synchronizer circuit capable of initiating a transmitted pulse whose time for transmission to and return from a target is determined as a measurement of target range by developing a second voltage having a phase shifted with respect to that of the fixed frequency /oltage, and deriving the transmitted pulse there- As a further object of my invention I wish to provide a circuit in which the repetition rate of a gating voltage pulse may be changed by passing only a predetermined number of the pulses.

A still further object of my invention is to provide. as a part of a synchronizing circuit, a phase shifting device which is capable of shifting the phase of a voltage compared with that of a fixed frequency voltage, one cycle of which is equal ,to an increment of range, through a plurality of, 360 changes without ambiguity.

Other objects and advantages of my invention will become apparent as the description proceeds.

In carrying out my invention, in a preferred embodiment thereof, I provide a circuit in which a fixed frequency voltage is generated whose period, on a basis of the speed of radio wave propagation, is equal to an increment oi range measurement. This voltage is delivered both to a phase shifting condenser and to a frequency divider, which in turn supplies a second phase shifter. From the unshifted and shifted voltages, separate short pulses, or pips, are generf ated which occur once during each cycle of the fixed frequency voltage. In like manner control or gating voltage pulses, or gates are generated from the output voltage of the frequency divider respectively before and after its phase has been shifted. The shifted and unshifted pips are then passed respectively through the shifted and unshifted gates generated from the reduced frequency voltage. The pip Whose phase is shifted, after a further reduction in its repetition rate,

supplied as a transmitter trigger pulse. Calibra tion of the phase shifting condensers of the system provides a measurement of the transit time of the transmitted pulse, and voltages are generated, under-,the control of the reflected signals, which may be used to actuate indicators and to drive servo mechanisms for automatically1 maintaining the phase shifting condensers in adjustment for range tracking.

Various gating and sweep wave voltages are generated in the circuit incidentally to the above functions and are delivered to other circuits as required.

The synchronizer circuit of the present invention is especially adapted for use with the indicating device disclosed in my copending patent application Serial No. 506,167, led October 14, 1943 which issued as Patent No. 2,512,703 on June 27, 1950.

A more comprehensive understanding of my invention will be afforded from the following detailed description when considered with the accompanying drawings, in which like reference numerals have been used throughout to designate like parts and in which carried on mount 2i.

Fig. 1 is a block diagram of a radar system in which my improved synchronizing circuit may be employed,

Figs. 2, 3, and 4 include a schematic diagram of the circuit embodying my invention,

Fig. 5 is a time sequence diagram oi the voltage wave forms generated within the circuit illustrated in Figs. 2, 3 and 4, for producing the required pulses, and

Fig. 6 is a voltage wave form diagram illustrating the principles of operation of that portion of the circuit employed for automatic ranging.

While my invention is not limited to any one application it is adaptable to radar apparatus and its use in connection with such a system will be illustrated for the purpose of developing the requirements which it is designed to meet.

In this Iparticular application definite values will be assigned to ranges, repetition rates, frequencies, pulse durations, etc., in order that the interrelation of each may be clearly shown. It is to be understood however that my invention is not limited to the values used nor are they to be construed as restricting its scope.

In the radar system illustrated in Fig. 1, the known speed of radio wave propagation is utilized to determine the range of a target i 5 located in space. The area in which targets are likely to be found is scanned by radio waves in the following manner. A wave pattern, made by the rotation of a lobe I8 about an axis i8, is transmitted from a dipole antenna (not shown) which is rotated within a parabolic reflector i3 Mount 2l is supported for 360 rotation on trunnion 22 and parabolic reflector I8 is movable vertically so that elevation mnning is provided as well as azimuth scan- The radio waves forming the beam I8 are generated in transmitter 23 and conducted to the antenna for radiation by conductor 24. They are received by the same antenna as waves reected Vfrom the target i5 and fed to a receiver 25, by conductors 24 and 28.

Transmission is initiated in transmitter 23 by a trigger pulse which is supplied from synchronizer 21 through line 28. A sweep wave gate is also supplied over line 29. A narrow gate is generated in the synchronizer 21 for delivery to receiver 25 over line 3| and the latter element ,supplies the former with video signals over line 32 which are used by the autoranging network of the synchronizer 21. Video signals are likewise 'transmitted to an indicator 33 over conductor .34'. A part of the xed frequency voltage generated in synchronizer 21 is delivered to indicator l33 yover conductor 34, which circuit also receives sweep gating voltage pulses from the same source by way of conductor 35.

The generation of the various voltages men- 'tioned above in connection with the system is,

as stated before, a function of synchronizer 21, which, as an embodiment of my invention, is illustrated in Figs. 2, 3, and 4.

In the above described radar system the maximum range may be taken as 50,000 yards. which on the basis of the known speed of radio waves 'and the desired use of a 2000 yard range increment, would dictate the use of a fixed frequency voltage of 81.94 kilocycles, one cycle thereof corresponding to a time delay of 12.2 micro-seconds, or 2000 yards of range.

Such a voltage is obtained from the fixed fre- 'quency generator 38 (Fig. 2) in which electronic discharge element 31 and its associated connections operates as a crystal oscillator with an output of 81.94 kilocycles. A similar element 3l which operates vas a buffer, receives the output of oscillator 31 on its control grid^39 and serves to isolate the oscillator against changes in load and to improve the wave form of its output as takenfrom its plate 4i.

The 81.94 kilocycle voltage from generator 35 is taken from the secondary winding of a transformer 42, whose primary winding is connected in the plate circuit of tube 38, for delivery to a frequency divider network 43 and over line 44 to a phase shifting condenser 45.

The ultimate function of frequency divider 43 is to decrease the Yrepetition rate of the transmitters output, which is accomplished by reducing the 81.94 kilocycle voltage through a series oi' divisions. Y

This voltage, received on grid 48 of element 41, is divided on a 5:1 ratio as follows. Element 41, illustrated as a pentagrid converter, is connected to modulate the 81.94 kilocycle input on grid 48 with a voltage having a frequency of 65.55 kilocycles (t of 81.94) received on grid 48 to furnish a difference frequency of 16.39 kilocycles (1/5 of 81.94) on plate 49. This latter voltage of 16.39 kilocycles is then fed to grid 5i of element 52, which is connected to act as a harmonic generator. where it is multiplied by four to furnish at plate 53 the 65.55 kilocycle voltage required by modulator 41.

Thus a 16.39 kilocycle voltage is delivered to grid 54 of element 55, which together with element 58, is connected in identical manner to operate as a second 5:1 frequency divider to furnish a 3278 cycle voltage at plate 51. From this point it is delivered through a phase shifting bridge 53 to grid 59 of amplifier 8l. The output of amplifier .8| is passed through filter 82 and thence over line 53 to a 3278 cycle phase shifting condenser 84 (Fig. 3).

The xed frequency voltage (81.94 kilocycles) produced by generator 38 is taken from the phase shifting circuit 44 over line 55, to amplifier 58, from which point it is delivered through transformer and over line 34 to indicator circuit 33 (Fig. 1).

It will be recalled that one cycle of the 81.94 kilocycle voltage corresponds to a time delay of 12.2 micro-seconds or a distance of 2000 yards insofar as the illustrated application is concerned. To provide for the measurement of these time delay increments it is proposed to shift the phase of the fixed frequency voltage in a manner which will eliminate ambiguity over a series of cyclical changes. Such is the function of the phase shifting condensers 45 (Fig. 2) and 84 (Fig. 3).

In the former the four stator plates 81 of the condenser are fed equal 81.94 kilocycle voltages from the secondary windings of transformer 88 with phase shifts of 0, 90, 180 and 270. 'I'he rotor 59 is shaped to deliver a constant output voltage whose phase shift from the input corresponds to the angular position of shaft 1I.

Since it is proposed to measure distance by utilizing the time delay between a pulse, or pip, generated from the unshifted 81.94 kilocycle voltage and a similar one generated from the 81.94

kilocycle voltage whose phase is shifted by condenser 45, it is necessary that the degree of shift be measurable. Accordingly, the condenser is so designed that one revolution of rotor 89 produces a phase rotation of 360 at 81.94 kilocycles, which is equivalent to a time delay of 12.2 microseconds, or 2000 yards range.

Obviously thev phase shift produced by condenser 45 becomes ambiguous after one revolution. since one pip will be generated for each cycle of the 81.94 kilocycle voltage. If the circuit is to be adaptable to uses requiring measurements in excess of 12.2 micro-second time delay, for example in the 50,000 yard radar system herein described for illustrative purposes, this ambiguity must be removed.

For this purpose a second phase shifting condenser 84 (Fig. 3) is provided which is geared to condenser 45 by shafts 12 and 18 through a. reduction gear 14. In keeping with the illustrative values previously established the ratio of reduction of gear 14 is 25:1 so that a 25 rotation of condenser 45 produces va 1 rotation of condenser 84.

Unlike condenser 45 which receives an 81.94 Y

kilocycle voltage, condenser 84 is supplied with the 3278 cycle voltage from frequency divider 43 (Fig. 2). This voltage from line 88, is taken from the secondary windings of a transformer and fed to stator plates 18 of condenser 84. Here the plates 18, the rotor 11, and shaft 18 are designed as are those of condenser 45.

Since the frequency of the voltage applied to condenser 84 is one-twenty-fifth of that applied to condenser 45, and since, through the action of reduction gear 14, the corresponding angular rotation of the former is one-twenty-fth of the latter, a gating voltage pulse, or gate, derived from .the,3278 cycle output of condenser 84 will be synchronized with the pipsgenerated from the 81.94 kilocycle output of condenser 45 'and may be used to select one of them. Thus ambiguity begins only after one complete revolution of condenser 84, equivalent to a time delay of approximately 305 micro-seconds, or in terms of range, 50,000 yards, while the degree of accuracy is determined by the finer adjustment of condenser 45.

As mentioned above, a pip is generated from the 81.94 kilocycle output of phase shifting condenser 45 and a gate from the 3278 cycle voltage output of condenser 84.

The pip is produced in a pulse generator 18 (Fig. 2), which includes a variable gain amplifier 8|, a power amplier 82 and a Peterson coil 88. This latter element generates positive and negative pips of approximately 1/8 micro-second duration which occur in time at the zero points on the 81.94 kilocycle sine wave. Feedback is provided pver line 85 to furnish amplifier 8| with bias for automatic gain control. A voltage divider to positive source in the grid circuit of element 8| provides a delayed A. V. C. action. Since the output impedance of condenser 45 is relatively high, a cathode follower 88, which may take the form of a triode, is interposed between the condenser and the initial stage of pulse generator 18 to drive the latter.

An identical pulse generator 81 (Fig. 4) is provided to generate pips from the fixed phase voltage (81.94 kilocycles), which is taken from a secondary winding of transformer 88 (Fig. 2) by line88. Within this branch (81) elements 88, 8| and 82 are connected to operate as do like elements 8|, 82, and 83 in generator 18.

Just as pips `are generated from the shifted and unshifted 81.94 .kilocycle voltages, so are gates generated from the 3278 cycle voltages, both shifted and unshifted.

Within a wave squaring circuit 83 (Fig. 3), comprising elements 84, 85, 88, 81, 88 and 88, the

shifted 3278 cycle sinusoidal voltage is squared cycles.

for delivery to a cathode-coupled multivibrator I 02 where it is converted into a 12.2 micro-second gate which is synchronized with the shifted 3278 A cathode follower |08 is interposed between condenser 84 and wave squarer 88 as an impedance matching device. lCathode-coupled multivibrator |02, which includes electronic discharge devices |04 and |00, delivers this 12.2 micro-second gating pulse from the plate circuit of its final stage |04 over line |08 to agating circuit |01 (Fig. 2).

An identical gate generator comprising a wave squaring circuit |08 (Fig. 4) and a cathodecoupled multivibrator |09, produces a 12.2 microsecond gate from, and in synchronization with, the unshifted 3278 cycle voltage. Wave squarlng circuit |08 made up of elements illustrated as trlodes ||2, ||3, ||4, ||5 and ||8, receives on the grid of its initial stage, by way of conductor I i1, the unshifted 3278 cycle voltage from transformer 15 associated with phase shifting condenser 84 (Fig. 3).` The output of multivibrator |08 is taken from its final two stages ||8 and ||8, over line 2| for delivery to a gating element |22.

Recalling the requirements of the illustrative application, a maximum range of 50,000 yards was desired for the radar system. With this range as a basis, a triggering pulse voltage of 81.94 kllocycles was chosen, the period (12.2 micro-seconds) of one cycle thereof being equivalent in range to a distance of 2000 yards. To prevent ambiguity in the phase shifting circuits and to reduce the repetition rate of the trigger pulse, a reduction of frequency was made to produce a voltage of 3278 cycles, equivalent to onetwenty-iifth of the 81.94 kilocycles. Gating voltages, in the circuits just described, were then generated from the 3278 cycles through which the 81.94 kilocycle pips could be passed to reduce their repetition rate.

It is possible in some applications, and the same is true in the illustrative example, that the repetition rate of the transmitted pulse need be reduced further than that required to give a suiiicient time delay, or extended range, without ambiguity.

Such a reduction therefore requires a decrease in the repetition rate of the gating pulse in dependently of the 3278 cycle voltage. This reduction is accomplished by a pip generator |23 (Fig. 4), a multivibrator |24 and the gating elements |01' (Fig.2) and |22 (Fig.4).

Pip generator |23, comprising elements |25 and |28, generates a pip at the tail of each fixed 12.2 micro-second pulse generated in |09 and received on the grid of tube |25 which is made to conduct for the duration of this pulse or gate. At the end of the gate, tube |25 is cut oil and a damped sine wave is set up in inductance coil |21 and its distributed capacitance. After the first half cycle, unilateral current conducting element |28 becomes conducting and dissipates the rest of the energy of the wave train set up in inductance coil |21. Multivlbrator |24 is so designed that element |28 thereof is conducting for one cycle out of three at 3278 cycles.` 'The output of discharge device |28 is therefore negative forone cycle out of three and is used as a gating pulse for valves |01 (Fig. 2) and |22', being delivered to them over conductor |3|. This gate' renders `these valves non-conducting for one cycle out of three thereby passing only one gate out of three passed respectively by gating elements |01 and |22. It is to be notedthatthe gating pulse applied to elements |01' and |22' "opens" and "closes at the ends of the 12.2 micro-second fixed phase gates. It will therefore open at the end of one fixed 12.2 micro-second gate; pass the next succeeding variable phase 12.2 micro-second gate and the next xed phase 12.2 micro-second gate; and will then close.

-Electronic valve |32 (Fig. 2) is rendered conducting by the 12.2 micro-second gate received from element |01 for only one cycle out of three (at 3278 cycles), since valve |01 passes only one such gate out of three. Consequently, valve |32 passes only one out of every seventy=five ya micro-second pips generated in pulse generator 19 and received therefrom over line |33. The pips, thus passed, trigger a blocking oscillator |34 which in turn produces a transmitter trigger pulse having a repetition rate of 1093 cycles, equal to that of the pips passed, or one-third of 3278 cycles. These transmitter pulses are taken from blocking oscillator |34, through transformer |35 and delivered over line 28 (Fig. 1) to transmitter 23, to perform one of the primary functions of the circuit.

The variable phase 12.2 micro-second gate is taken from the plate circuit of element |01 by conductor |36 and fed to a repeater tube |31 where it is repeated for delivery to indicator 33 (Fig. 1) over line 35.

A 2 micro-second gate, used by receiver 25 of the radar system illustrated in Fig. 1, is employed to limit the target area of that device. Since it must have a repetition rate equal to that of the transmitted pulse, it is produced in a manner similar to that of the transmitter trigger pulse, by electronic switching device |38 (Fig. 4) and blocking oscillator |39.l

Here in a manner identical with that describing the generation of the transmitter trigger pulse, a 2 micro-second gate is produced having a repetition rate of 1093 cycles. Thus, the gate taken from multivibrator |24 over conductor |3| is fed to the grid of element |22', which turns it on to pass only one out of three of the 12.2, microsecond gates derived from the unshifted 3278 cycle voltage in multivibrator |09 and received on the grid of valve |22. Accordingly, the 12.2 micro-second gate, now having a repetition rate of 1093 cycles, controls valve |38 t'o pass, at this repetition rate, the pips generated in network 81 from the unshifted 81.94 kilocycle-voltage. These pips, taken from generator 01 by line |4|, are passed by valve |38 at a repetition rate of 1093 cycles and trigger theblocking oscillator |39 which generates the desired 2 microsecond gate. This gate is passed through pulse transformer |42 from whose secondary winding it ls delivered to autoranging network |43 (Fig. 3) and to the receiver 25 (Fig. 1). Conductor |44 serves network |43, and receiver 25 issupplied through a repeating tube |45 and over line 3|.

A repeater tube |46 and pulse transformer |41 are used to repeat the fixed phase 12.2 micro-second gate into indicator 33 (Fig. l) over line'35. This gate is taken from the plate of element |22 by line |48 for application to the grid of repeater |46.

In connection with its application to the radar system illustrated in Fig. l, one of the functions of the synchronizer is to condition that device for automatic range tracking. This result is accomplished in that branch of the synchronizer circuit illustrated in Fig. 3 and designated by the numeral |43. Here two mixing elements illustrated as pentagrid converters |49 and |5I, are

utilized as coincidence tubes. Video signals are received from receiver 25 (Fig. 1) over line 3|. They are applied directly to control grid |52 of mixer |5| and through a, 2 micro-second delay line |53 to grid |54 of element |49. The 2 microsecond gate received from blocking oscillator |39 (Fig. 4) over line |44 is delayed in a delay line |65 before it is applied to grids |56 and |51 of tubes |5| and |49, respectively. The outputs of mixers |49 and |5| are taken from their respective plate circuits and fed to the cathodes of triodes |58 and |59, respectively, which are connected to operate asunilateral current conducting devices. VThe outputs of rectifiers |59 and |58 are delivered respectively to the grids I6! and |62 ci elements |33 and |64 whose cathods are connected across a common cathode resistor |65. The output from the plate of tube |64 is used to ignite the gaseous element |66 and condenser |61 is charged through it and resistor |68. The voltage across condenser |61 is then fed to servo-amplifier |89 over conductor |1| where it is amplified for driving servo motor |12, to condition the range condensers 64 and 45 (Fig. 2). Through circuit |43 these phase 'shifting condensers are adjusted for autoranging in accordance with the signals received over line 3| as will be explained in connection with the description of the entire circuits l operation which follows.

Since a majority of the synchronizers components are conventional circuits and therefore requireno detailed explanation of their operation and since all pertinent operational details have appropriately been stated as the element concerned was described, only a general recital of the circuits over-all operation will be made. This will be presented with reference to Figs. 5 and 6 which depict the wave forms of the various voltages produced in the synchronizer circuit.

The fixed frequency voltage represented by sine wave in Fig. 5 is generated in generator 36 (Fig. 2) Sine wave whose phase remains xed, is transmitted over line 44, through transformer 68 and over line 88 to pip generator 81 (Fig. 4). where a positive pip, illustrated as pip is generated for each cycle of the fixed frequency voltage to occur 1n point of time when this voltage passes from positive vto negative through its zero point such as |13. Sine wave is shifted in f phase in condenser 45 to yield sine wave 2.

A similar pip, pip 2, is generated from each cycle ofvsine wave 2, whose phase is shifted, to

occur at its zero point |14. This pip is developed in generator 19 (Fig. 2), the fixed frequency voltage being taken from transformer 68 through vphase shifting condenser 45.

A third sinusoidally varying voltage, shown as y sine 3, is produced by passing a portion of the voltage generated at 36 through the frequency divider 43. This voltage,.taken from the divider by line 63, is delivered -to transformer 15 (Fig. 3) where a portion of it (unshifted) is routed over line ||1 to wave squaring circuit |08 (Fig. 4) and a portion to phase shifting condenser 64 where a fourth sine wave, sine 4, is produced.

By means of the wave squaring circuit |08 (Fig. 4) and multivibrator |09, a gate |15, gate 3, is developed from sine 3 which is synchronized to occur in point of time at its zero point |16, with one zero point, such as |13, of the voltage, sine and with a pip, such as |11, generated from sine Similarly, by means of wave squaring circuit 93 (Fig. 8) and multivibrator |02, a gate |18 (gate 4, Fig. is generated from sine 4, whose phase has been shifted at condenser 64, to occur at zero point |14 and with pip |8| derived therefrom.

To effect a further reduction in repetition rate, .a gating voltage is produced by pip generator |23 (Fig. 4) and multivibrator 24 which is usedby elements |22 and |22 and |01 (Fig. 2) and |81' to pass only a selected number of gates such as |15 and |18, respectively. These gates in turn. through the action of elements |38 and |32, pass only a selected number of pips, such as |11 and I8| of pip and pip 2, equal to the repetition rate of the selected gates |15 and |18.

By this Vgating process pips such as |82, are produced from sine I whose repetition rate is reduced from the frequency thereof to one which includes the decrease .in frequency divider 43 and that produced by the gating elements |22, |22 and |38.-

Similar pips, such as |83. having the same repetition rate, are generated from the phase shifted voltage.

These pips, |82 and |83, are used to trigger blocking oscillators |39 and |34, respectively, Blocking oscillator |34 (Fig. 2) triggers a transmitter to produce a transmitter pulse |84, and oscillator |39 (Fig. 4) generates the narrow gate |85.

Thus, in the radar system illustrated in Fig. 1, the transmitter 23 is triggered to produce transmitter pulse |84, which has a repetition rate of 1093 cycles and whose phase may be advanced or retarded as indicated by the double arrow. These transmitted pulses are then received as reflected signals from the target by receiver 25. By suitable indicating means provided in indicator 33 it is possible to adjust the phase shifting condensers 45 (Fig. 2) and 64 (Fig. 3) until the reected signal |84 is received by receiver in coincidence with the gate |85 from synchronizer 21, whose phase is fixed. Since phase shifting condenser 45 is so designed that one revolution of its rotor is equivalent to a time delay of 12.2 micro-seconds (a shift of one cycle of the 81.94 kilocycle voltage, or 2000 yards range) and since the number of degrees of phase shift necessary to bring signals |84 and |85 into coincidence is a measure of the time required for signal |84 to go out to target I5 and back to the detector, the angular displacement of rotor 69 in phase shifter 45 is, on a basis of speed of radio wave propagation, a measure of range.

At this juncture, it should be recalled that the channels for producing the transmitter trigger pulse and the receiver gate are identical with the exception of the phase shifting condensers. Thus, any change in voltage, temperature or the like, which effects a change of phase in one channel will produce a compensating phase shift in the other channel, and the errors produced by such changes are accordingly eliminated. 'I'his increases the accuracy of the systems ranging apparatus and constitutes one of the princpal advantages of my improved synchronizer circuit.

Now, obviously if the target is moving away from or toward the detector the transit time of signal |84 will be changing continuously and it will be necessary to change the setting of phase shifting condensers 45 and 64 to `compensate for this change in range.

This adjustment of the system's range sensing mechanism is called range tracking and may be accomplished manually or automatically.

Automatic range tracking is a function of the synchronizer and is accomplished by the autoranging circuit |48 (Fig. 3) whose operation will be explained with the aid of Fig. 6.

Here the narrow gate |85, enlarged for purposes of illustration, is shown in relationship with reflected signal |88.

In circuit |43 video signal |84 from receiver 25 is delayed in delay line |53 to produce delayed ignal |88. Similarly narrow gate is delaye \in delay line |55 to produce delayed gate |81. Within the mixers |49 and |5| which act as coincidence tubes, delayed signal |86 and undelayed signal |84 are respectively mixed with delayed gate |81.

If range synchronism isperfect, gate |81 will fall exactly between signals |84 and |86, as shown, and coincidence signal curves I and 2 will be produced as the outputs of mixers I5| and |49, respectively. For this condition coincidence signals such as |88 and |89 will be developed whose magnitudes are equal.

Now as the target moves, signals |84 and |88 will be advanced or retarded with respect to xed gate |81 and coincidence signals such as |9| and |92 will obtain. Within the remaining part of the circuit a voltage is developed across condenser |61 whose rate of change is proportional to the potential difference of signals |9| and |92. This voltage as amplied in servo amplier I 89 is used to drive servomotor |12 which in turn positions phase shifting condensers 64 (Fig. 3) and 45 (Fig. 2) to advance or retard signals |84 and |86 until they again bracket signal |81, thereby bringing the system into range synchronism.

Since the range rate of servomotor |12 is proportional to servo amplier input, or the voltage developed across condenser |81, the servo range rate will thus be corrected toward the proper value. Direction will be provided by the polarity of the amplier input about a reference.

Should the radar signal fade out. the output of amplifier |64 will fall to approximately zero, the charge on condenser |61 will remain constant and the range rate previously established will be maintained.

Modifications of my invention are of course possible and may present themselves in view of the foregoing disclosure. Accordingly the descriptions and representations herein made are to be considered illustrative and nowise in a restricted sense and the spirit and scope of my invention to be regarded as of such breadth as is defined by the appended claims.

What is claimed is:

1. In combination, a rst source of fixed-frequency voltage, first adjustable phase-shifting means connected to said first source and adapted to supply a second voltage identical in frequency but displaced in phase relative to said xedfrequency voltage, separate means for generating rst and second series of pulses each having a periodicity equal to the frequency of said fixedfrequency voltage and having a given phase relationship respectively to said fixed-frequency voltage and to said second voltage, a source of a third voltage having a frequency which is a submultiple of that of said fixed-frequency voltage, second adjustable phase-shifting means connected to said third-voltage source and adapted to supply a fourth voltage identical in frequency but displaced in phase relative to said third voltage, separate means for generating third and fourth series of pulses each having a periodicity li equal to the frequency of said third voltage and having a given phase relationship respectively to said third and fourth voltages, means for con- 'trolling the ltransmission of said first and second VVVquency voltage, first adjustable phase-shiftingVY means connected to said first source and adapted to supply a second voltage identical in frequency but displaced in phase relative to said fixedfrequency voltage, separate means for generating rst and second series of pulses each having a periodicity equal to the frequency of said fixed-- frequency voltage and having a given phase relationship respectively to said fixed-frequency voltage and to said second voltage, a source of a third voltage having a frequency which is a sub- 'multiple of that of said fixed-frequency voltage, second adjustable phase-shifting means connected to said third-voltage source and adapted to supply a fourth yvoltage identical in frequency but displaced in phase relative to said third voltage, separate means for generating third and fourth series of pulses each having a periodicity .qual to the frequency of said third voltage and having a given phase relationship respectively to said third and fourth voltages, means for gen-` erating a fth series of pulses having a periodicity which is a submultiple of that of said fourth series of pulses, means for controlling the transmission of said ilrst and second series of pulses respectively by said third and fth series of pulses, means for subjecting said controlled second series of pulses to an unknown time delay, and means for indicating time coincidence between said controlled first series of pulses and said delayed controlled second series of pulses, whereby the settings of said first and second phase-shifting means provide a measure oi' said -unknown time delay.

3. In combination, a source of fixed-frequency voltage, adjustable phase-shifting means connected to said source and adapted to supply a voltage identical in frequency but displaced in phase relative to said fixed-frequency voltage, separate means for generating first and second series of pulses each having a periodicity `equal in the frequency of said fixed-frequency voltage 'and having a given phase relationship respecassassin l2 4. In combination, a first source of xedquency voltage, first adjustable phase-shifting means connected to said ilrst source and adapted to supply a second voltage identical in frequency but displaced in phase relative to said xedfrequency voltage, separate means for generating first and second series of pulses each having a periodicity equal to the frequency of said fixed-frequency voltage and having a given phase relationship respectively to said fixed-frequency voltage and to said second voltage, a source of a third voltage having a frequency which is a submultiple of that of said fixed-frequency voltage, second adjustable phase-shifting means connected to said third-voltage source and adapted to supply a fourth voltage identical in frequency but displaced in phase relative to said third voltage, separate means for generating third and fourth series of pulses each having a periodicity equal to the frequency of said third voltage and having a given phase relationship respectively to said third and fourth voltages, means for generating a fifth series of pulses having a periodicity which is a, submultiple of that of said fourth series of pulses, means for controlling the transmission of said first and second series of pulses respectively by said third and fifth series of pulses, ,means for subjecting said controlled second series of pulses to a variable time delay, and means actuated by the time displacement between said controlled flrst series of pulses and said delayed controlled second series of pulses for automatically varying the setting of said phase-shifting means to provide a continuous measure of said variable time delay.

5. In combination, a. source of fixed-frequency voltage, adjustable phase-shifting means connected to said source and adapted to supply a voltage identical infrequency but displaced in phase relative to said fixed-frequency voltage, separate means for generating first and second series of pulses each having a periodicity equal to the frequency of said fixed-frequency voltage and having a given phase relationship respectively to said fixed-frequency voltage and to said phaseshifted voltage, means for subjecting said second series of pulses to an unknown time delay, and a servo motor responsive to phase variations between said rst series of pulses and said delayed` second series of pulses for -activating said adjustable phase-shifting means, thereby providing an indication of said unknown time delay.

JEFFERSON R. WILKERSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

